Field of Invention
The invention relates generally to hydrofluorocarbon compositions. More particularly, the invention relates to blends of one or more hydrofluorocarbons, trifluoroiodomethane (CF3I) and hydrocarbons, as well as methods for using these compositions in applications such as the recharging of refrigeration systems. and for its use in replacing a chlorofluorocarbon or hydrochlorofluorocarbon in a refrigeration system.
Description of the Related Art
Chlorofluorocarbons (CFCs) and hydrochlorofluorocarbons (HCFCs), such as dichlorofluoromethane (R-12), monochlorodifluoromethane (R-22), and azeotropic mixtures of monochlorodifluoromethane and chloropentafluoroethane (R-115) (known as R-502), have conventionally been used as refrigerants in heating and cooling systems. However, the use of chlorine-containing refrigerants, such as chlorofluorocarbons (CFC's), hydrochlorofluorocarbons (HCFC's) and the like, as refrigerants in air-conditioning and refrigeration systems has become disfavored because of the ozone-depleting properties associated with such compounds.
New compounds have been developed as alternatives to CFCs and HCFCs. Hydrofluorocarbons (HFCs) and hydrofluorocarbon blends are of particular interest as such alternatives because they have properties that are similar to chlorofluorocarbons, including similar refrigeration characteristics, i.e. a vapor pressure that is plus or minus 20 percent of the reference refrigerant at the same temperature, chemical stability, low toxicity, non-flammability, efficiency in-use and low temperature glides. Unlike CFCs and HCFCs, HFCs do not damage the ozone layer, and thus are considered environmentally friendly. Moreover, HFCs generally possess a good efficiency in-use which is important, for example, in air conditioning and refrigeration where a loss in refrigerant thermodynamic performance or energy efficiency may have secondary environmental impacts through increased fossil fuel usage arising from an increased demand for electrical energy.
Some HFCs are known to be exceptional refrigerants, including, but not limited to, difluoromethane (R-32), 1,1,1,2,2-pentafluoroethane (R-125), 1,1,1-trifluoroethane (R-143a), 1,1,1,2-tetrafluoroethane (R-134a), and 1,1-difluoroethane (R-152a). Certain blends of two or more of these HFCs can also be used to achieve particular thermodynamic properties. Common HFC blends include an azeotrope-like blend of R-143a and R-125 (known as R-507A), a non-azeotropic blend of R-125, R-143a, and R-134a (known as R-404A), a non-azeotropic blend of R-32 and R-125 (known as R-410A), and a non-azeotropic blend of R-32, R-125, and R-134a (known as R-407C). These alternative refrigerants are available commercially from various sources including Honeywell, DuPont, Atochem and ICI.
Each of these HFCs or HFC blends can serve as a replacement for one or more CFCs or HCFCs. For example, R-134a can serve as replacement of R-12 in refrigeration and air conditioning applications such as chillers; R-404A and R-507A can serve as replacements for R-502 in most refrigeration applications, including high, medium and low evaporation temperature systems; R410A can serve as replacement of R-22 in new air conditioning and refrigeration equipment: and R-407C can serve as a replacement for R-22 in various air-conditioning applications, as well as in most refrigeration systems including chillers. The use of chlorine-containing refrigerants, such as chlorofluorocarbons (CFC's), hydrochlorofluorocarbons (HCFC's) and the like, as refrigerants in air-conditioning and refrigeration systems has become disfavored because of the ozone-depleting properties associated with such compounds. As a result, it has become desirable to retrofit chlorine-containing refrigeration systems by replacing chlorine-containing refrigerants with non-chlorine-containing refrigerants that will not deplete the ozone layer, such as hydrofluorocarbons (HFC's). In order for replacement materials to be useful in connection with refrigeration compositions, the materials must be compatible with a lubricant utilized in the compressor.
However, widespread commercial use of these and other HFC refrigerants has been hindered by the lack of commercially adequate lubricants. Refrigeration system designers are interested in how the lubricant behaves in the system so that they can design piping and other components to best manage lubricant return to the compressor. The behavior of a refrigerant on a lubricant entering the system can affect film characteristics on heat transfer surfaces, and thus energy efficiency performance. Generally, the first property considered is miscibility of the lubricant with the liquid refrigerant. Unfortunately, many non-chlorine-containing refrigeration fluids, including HFC's, are relatively insoluble and/or immiscible in the types of lubricants used traditionally with CFC's and HFC's, including mineral oils. In order for a refrigeration fluid-mineral oil combination to work efficiently within a compression refrigeration, air-conditioning or heat pump system, the mineral oil must be sufficiently soluble in the refrigeration liquid over a wide range of operating temperatures. Such solubility lowers the viscosity of the mineral oil and allows it to flow more easily throughout the system. In the absence of such solubility, mineral oils tend to become lodged in the coils of the compression refrigeration, air-conditioning or heat pump system evaporator, as well as other parts of the system, and thus reduce the system efficiency. Fluorocarbon-based fluids have found widespread use in industry for refrigeration system applications, including air-conditioning systems and heat pump applications as well, all of which involve compression refrigeration.
The HFC refrigerants that are replacing HCFC refrigerants have a different influence on lubricants, which affects both compressor durability and system performance. Specifically, mineral oil or alkyl benzenes, which have been used with conventional refrigerants such as R-12, R-502 and R-22, are immiscible with HFCs and must therefore be replaced with polyol ester (POE) or other synthetic lubricants. However, major development considerations for the synthetic lubricants remain, including miscibility, solubility, stability, electrical properties, lubricity and retrofitting requirements.
Since HFC are generally immiscible in conventional lubricants, retrofitting refrigeration or air conditioning systems with HFC refrigerants typically requires the drainage of as much of the lubricant oil as possible before introducing the new refrigerants with synthetic lubricants. This process often involves removing the compressor from the system so that the lubricant can be adequately drained. For these and other reasons, it would be highly desirable to retrofit a CFC or HCFC system with HFC without having to remove the system's lubricant. By not needing to replace the existent oil, such a retrofit would become a simple “drop-in” operation. That is, the existent refrigerant would be replaced with a new refrigerant without any further change in, or disassembly of, the system hardware.
U.S. Pat. No. 5,611,210 teaches fluoroiodocarbon blends with an additive selected from the group consisting of: alcohols, esters, ethers, fluoroethers, hydrocarbons, hydrofluorocarbons, and perfluorocarbons with boiling points between −150° C. and +2000° C. U.S. Pat. No. 7,208,098 discloses a lubricating composition for compression refrigeration containing a blend of a polyol ester and an alkylbenzene, however, CF3I is not taught. U.S. patent application 20050233934 teaches azeotrope-like compositions comprising tetrafluoropropene and trifluoroiodomethane and uses thereof, including use in refrigerant compositions, and refrigeration systems. U.S. 2006/0116310A1, U.S. Pat. No. 7,083,743 and WO 94/20588 show combinations of halocarbons and fluoroiodocarbons. US2003/0062508A1, U.S. Pat. No. 2,004,006, U.S. Pat. No. 2,005,015 and U.S. Pat. No. 6,428,720 show combinations of halocarbons and hydrocarbons.
Accordingly, there exists a need and an opportunity to resolve this solubility problem so that the refrigeration industry may retrofit systems without costly and time-consuming flushing to entirely remove conventional lubricants. Applicants have discovered that the miscibility of HFCs in conventional lubricants can be greatly increased by blending the HFCs with CF3I (trifluoroiodomethane) and hydrocarbons (HC). It has been unexpectedly found that HFCs blended with CF3I and HCs are generally more miscible in common lubricant oils than blends of HFCs alone. By utilizing such HFC/CF3I/HC blends, CFC or HCFC systems can be retrofitted without having to drain or replace the system's lubricants. In addition, it has been found that certain blends of HFCs, CF3I and HCs generally retain the thermodynamic properties that are important for refrigerants.